The present invention relates to a ferromagnetic material sputtering target that is used for the deposition of a magnetic thin film of a magnetic recording media, particularly for the deposition of a magnetic recording layer of a thermally-assisted magnetic recording media, and to an FePt-based ferromagnetic material sputtering target capable of achieving a stable discharge and reducing the generation of particles when sputtered with a magnetron sputtering equipment.
In the field of magnetic recording media as represented with HDD (hard disk drives), a material based on Co, Fe or Ni as ferromagnetic metals is used as the material of the magnetic thin film which is used for the recording. For example, Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloys with Co as its main component are used for the recording layer of hard disks adopting the longitudinal magnetic recording system. Moreover, composite materials of Co—Cr—Pt-based ferromagnetic alloys with Co as its main component and nonmagnetic inorganic grains are often used for the recording layer of hard disks adopting the vertical magnetic recording system which was recently put into practical application. In addition, a magnetic thin film of a magnetic recording medium such as a hard disk is often produced by sputtering a ferromagnetic material sputtering target having the foregoing materials as its components in light of its high productivity.
Meanwhile, the recording density of magnetic recording media is rapidly increasing year by year, and the current surface density of 100 Gbit/in2 is expected to reach 1 Tbit/in2 in the future. When the recording density reaches 1 Tbit/in2, the size of the recording bit will fall below 10 nm and, in such a case, it is anticipated that the superparamagnetization caused by thermal fluctuation will become a problem, and it is further anticipated that the currently used magnetic recording medium; for instance, a material with higher magnetic crystalline anisotropy obtained by adding Pt to a Co—Cr-based alloy, or a medium in which B is further added to the foregoing material to attenuate the magnetic coupling between the magnetic grains, will no longer be sufficient. This is because, for grains to stably behave ferromagnetically at a size of 10 nm or less, the grains need to possess even higher magnetic crystalline anisotropy.
In light of the above, an FePt phase having an L10 structure is attracting attention as a material for use in an ultrahigh density recording medium. Moreover, since an FePt phase having a L10 structure yields superior corrosion resistance and oxidation resistance, it is expected to become a material that can be suitably applied as a recording medium. The FePt phase has an order-disorder transformation point at 1573 K, and has a L10 structure even when an alloy is hardened from a high temperature due to the rapid ordered reaction. Furthermore, in connection with using the FePt phase as a material for use in an ultrahigh density recording medium, demanded is the development of technology for dispersing the ordered FePt grains, in a magnetically separated state, while densely aligning the orientation thereof as much as possible.
In light of the foregoing circumstances, a magnetic thin film having a granular structure in which the FePt magnetic grains having an L10 structure are magnetically separated from each other through the interposition of nonmagnetic materials such as carbon is being proposed for use in a magnetic recording medium of next-generation hard disks adopting the thermally-assisted magnetic recording system. This magnetic thin film having a granular structure has a structure in which the magnetic grains are magnetically insulated through the interposition of nonmagnetic substances. Documents related to granular-type magnetic recording media and other related publications include, for example, Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7 listed below.
The foregoing magnetic recording layer is configured from a magnetic phase such as an Fe—Pt alloy and a nonmagnetic phase that separates the magnetic phase, and carbon is effective as the nonmagnetic phase material. While this kind of magnetic recording layer is normally formed via the sputter deposition method, a ferromagnetic material sputtering target containing carbon entails the following problems; namely, carbon is prone to aggregate, the target is difficult to be sintered and, when sputtered with a magnetron sputtering equipment, causes an abnormal discharge during sputtering, and thereby generates particles (contaminants that adhere to the substrate).    Patent Document 1: JP 2000-306228 A    Patent Document 2: JP 2000-311329 A    Patent Document 3: JP 2008-59733 A    Patent Document 4: JP 2008-169464 A    Patent Document 5: JP 2012-102387 A
Patent Document 6: JP 2011-208265 A    Patent Document 7: International Publication No. WO/2012/086335